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# What is the median value of the set R, if for every term in

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What is the median value of the set R, if for every term in [#permalink]  28 Jul 2006, 19:32
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75% (01:16) correct 25% (00:00) wrong based on 4 sessions
What is the median value of the set R, if for every term in the set, Rn = Rnâ€“1 + 3?

1) The first term of set R is 15.
2) The mean of set R is 36.
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(C) for me

It is question on arithmetic progression.

ST1. R1=15 is not suffiecient because we don't know n.

ST2. For arithmetic progression, Mean=(R1+Rn)/2
So, (R1+Rn)/2=36. Still not suuficient without knowing R1 and n.

Combining two we can solve for n. So, (C) is sufficient
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I think its C.

To know the median we need to know the number of terms.

St1: Can't tell anything.: INSUFF

St2: Can't tell anything. : INSUFF

Combined:
Sum of all terms = 36n = (n/2)(15+(n-1)*3)
n = 20
Can find out the 10th and 11th term and median can be found. : SUFF
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Reconsider this.. this one has trick!
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freetheking wrote:
Reconsider this.. this one has trick!

you are correct. its B.

in this case, always median = mean.
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OA is B
OE:
The set Rn = Rnâ€“1 + 3 describes an evenly spaced set: each value is three more than the previous. For example the set could be 3, 6, 9, 12 . . .

For any evenly spaced set, the mean of the set is always equal to the median. A set of consecutive integers is an example of an evenly spaced set. If we find the mean of this set, we will be able to find the median because they are the same.

(1) INSUFFICIENT: This does not give us any information about the value of the mean. The only other way to find the median of a set is to know every term of the set.

(2) SUFFICIENT: The mean must be the median of the set since this is an evenly spaced set. This statement tells us that mean is 36. Therefore, the median must be 36.

source mgmat.
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